This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-18891, filed Jan. 27, 2000 and No. 2000-174059, filed Jun. 9, 2000, the entire contents of which are incorporated herein by reference.
The present invention relates to a system for monitoring the operation state of a number of lamps to be installed on runways, taxiways or others in the airport.
An airport lamp detection system for monitoring and controlling the operation state of a number of lamps in the airport using the power line transport technology is known. In an example of such system, as shown in FIG. 1, a host station (not shown) and, respectively through a rubber transformer 63, terminals (slave stations) 64 are connected in series to a power line 62 derived from a fixed current generator (CCR) 61 connected to an alternative current source.
By the way, in such airport lamp monitoring and control system, when a lamp has burned out, a relay switch SW to be connected to that lamp 65 is put OFF, and magnetic saturation phenomenon is provoked by making the secondary side of the rubber transformer 62 open. In short, injection operation of lamp filament cut occurrence signal is performed. On the other hand, while the lamp is normal, signal extraction operation is performed to extract a control signal to be superposed on the power line 62.
Now, the output current rise of the fixed current generator 61 increases generally in a rapid state. However, when the lamp has burned out, it becomes slow until the magnetic saturation of the rubber transformer 63, showing a rise waveform slower than when the lamp is normal. Consequently, a primary side voltage waveform of the power line 62 shows a waveform rising suddenly after a period of time (saturation time) a where the output current rises slowly as shown in FIG. 2. Moreover, when a lamp has burned out, the saturation time a varies according to the level of the waveform rise 66 protruding when the relay switch is open, and consequently, the rise waveform varies.
Now, the host station or higher order system side detect the lamp filament rupture by monitoring the saturation state of the output current form the fixed current generator 61. However, in practice, the detection of lamp filament rupture based on the signal injection operation is sometimes difficult, and the decrease of detection accuracy can not be avoided, because it is difficult to identify the saturation time xcex1, and the rise 66 is not constant. This is because, signals of normal operation and lamp filament rupture are detected by the difference of area through the time integration, as magnetic saturation time of the rubber transformer 63 is not constant. In short, as shown in FIG. 2, the detection accuracy has been hardly improved, because the signal waveform per se during the normal time was unstable, and unreliable.
On the other hand, the fixed current generator in the aforementioned monitoring and control system, is the one designed to supply the power line with power of fixed current and, more concretely, as shown in FIG. 3, adopts a method to select a current waveform S2 of high amplitude between a low amplitude current waveform Si and the high amplitude waveform S2 through the phase control at an appropriate phase angle (60 degrees for example) from the zero cross point of the low amplitude current waveform S1, using a thyristor, output a predetermined fixed current (6.6 A for example) defined beforehand to be used for lamps or other airport equipment, and supply to the power line. Therefore, the current immediately after the phase control varies generally in a rapid rise state, presents a high frequency equal or superior to 50 Hz/60 Hz in respect of frequency, transits to a standard waveform (sinusoidal wave) of 50 Hz/60 Hz when it attains the high amplitude current waveform, but happens to be unstable immediately after this transition.
There, conventionally, in the case of transmitting a required signal using a power-line carrier, control, monitoring or other signals are transmitted using the power-line carrier, by modulating them with a predetermined frequency from a power line mode which is a part of signal processing system, for the high amplitude waveform S2 at such a timing to avoid the low amplitude current waveform on the power line and rapid rise portions immediately after the phase control, and further, unstable portions during the transition to the high amplitude current waveform, namely noise generating portions.
However, the aforementioned monitoring and control system aims only to transmit a signal at an appropriate timing, noise still generates from the fixed current generator by the phase control, and under the influence of this noise, the reception sensibility of host station and respective terminals deteriorates considerably. In addition, this noise is a spike noise generated like as impulse, and moreover, it is extremely difficult to eliminate, as the noise generation point varies according to the tap position (phase control angle) for adjusting the lamp brightness.
Also, in the host station and respective terminals, the control signal and monitoring signal are carried by the power line, using a power line circuit including power line, rubber transformer or the like; however impedance due to LC exists in the power line circuit, and this impedance absorbs signal carried by the power line. This is caused mainly by resonance phenomenon between the rubber transformer reactance L component and the power line and ground capacitance, and there exist abnormal attenuation points of signal carried by the power line. As the result, terminals at the position corresponding to the abnormal attenuation point drop remarkably in their reception sensibility due to the attenuation of carried signal.
Especially, in the case of power-line carrier, abnormal attenuation point is an inevitable problem, because rubber transformers constituting a number of reactance components are installed in the power line circuit. And further, the installation of rubber transformer depends on the lamp location in the airport, and can not be decided arbitrarily, the abnormal attenuation amount increases inconveniently according to the installation mode.
It is an object of the present invention to provide a system for monitoring the lamp operation state without using magnetic saturation of rubber transformer, and an airport lamp monitoring system permitting a high quality transmission, without being influenced by the power line circuit construction conditions.
To solve the aforementioned problems, the present invention relates to an airport lamp monitor system, wherein a host station connected to a higher order system and respective terminals for monitoring individually the airport lamp via a rubber transformer are connected in series to a power line derived from a fixed current generator, the host station transmitting control signal to the respective terminals for using power-line carrier based on a signal from the higher order system, and the respective terminals transmitting a lamp monitoring signal to the host station by using power-line carrier, the host station and terminal comprise:
a signal injection section for intermittently injecting the control signal and lamp monitoring signal to the power line at a predetermined cycle within a predetermined time from the zero cross of power source waveform of the power line; and
a signal extraction section including zero cross detection means for detecting the zero cross of power source waveform of the power line and signal reception detection means for receiving the control signal and lamp monitoring signal injected to the power line based on a specific frequency component within a predetermined time from the zero cross detection by this zero cross detection means.
According to the present invention, adopting the aforementioned configuration, it is possible to avoid the prevention of magnetic saturation, because for both the host station and respective terminals, the signal injection section injects intermittently the control signal and lamp monitoring signal to the power line at a predetermined cycle within a predetermined time from the zero cross of power source waveform of the power line and, on the other hand, the signal extraction section can receive the lamp operation state or the like with a high accuracy, by receiving the control signal and lamp monitoring signal injection to the power line based on a specific frequency component within a predetermined time from the zero cross detection.
In order to solve the aforementioned problem, the present invention is characterized by that a filter apparatus comprising a LC resonance circuit resonating the frequency used for the power-line carrier is provided on the output side power line of the fixed current generator, and noise generated from the fixed current generator and signal of the frequency used for the power-line carrier at the output side of the fixed current generator between the host station and each terminal are respectively separated.
The present invention, adopting the aforementioned configuration, installs a filter apparatus including a LC resonance circuit resonating the frequency used for the power-line carrier and sends noise generated from the fixed current generator to the power source generation side by the filter apparatus, and on the other hand, sends signal transmitted and received between the host station and the terminal to the host station and terminal side by means of the filter apparatus, thus separates noise and signal completely, improving the signal transmission quality.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.